Synchronizing control



July 13, 41948. J..w. BRAKE sYNcaRonIzING CONTROL Filed Jue 21. 1946 2Sheets-Sheet 1 ...fil

Nvt-'ufo @james D rake (HT-roma# Patented July 13, 1948 James W. Drake,Rockford, Ill., assignor to Woodward Governor Company, Rockford, Ill., acorporation of Illinois Application June 21, 1946, Serial No. 678,213

11 Claims.

This invention relates to a mechanism for automatically synchronizingthe rotary speeds of one or more vpower drivenslave units, such as theprime movers of a multiengine aircraft, with that of a master power unitthe speed of which, as well as that of the slave units, may be adjustedunder manual control.

One object is to provide a synchronizing control having a novel meansfor limiting the range of speed adjustment thereby so as to avoid widevariation in the speed of any slave unit following a failure of themaster unit.

Another object is to provide for centering of the range limiting means`during each manual adjustment of the speed settings of the power units.

The invention also resides in the novel construction and arrangement ofthe range limiting means and thel manner in which it is renderedoperative and inoperative selectively.

Other objects and advantages of the invention will become apparent fromthe following detailed description taken in connection with theaccompanying drawings, in which Figure 1 is a schematic view and wiringdiagram 'of a plurality of -power units adapted to be synchronized inaccordance with the present invention.

Fig. 2 is a vertical sectional view of the principal parts of the rangelimiting means.

Fig. 3 is a perspective view of the range limiting means.

Fig. 4 is a fragmentary elevational view of the parts of the rangelimiting means.

In the drawings, the invention is shown for purposes of illustrationincorporated in a system for manually adjusting the speeds of aplurality of internal combustion engines and automatically synchronizingthe speed of one or more engines S with that of a master engine uM.Herein, the speeds of the power units are controlled'by individualgovernors III which, in the case of aircraft engines, eilect ay speedregulation by adjusting the pitch of propellers II driven by theengines. This may be accomplished by applying hydraulic pressure4controlled by the governor to a servomotor I2 for turning the propellerblades on their longitudinal axes. The governor I on each slave andmaster engine includes a head I3 driven by the engine and 4pivotallysupporting iiyballs I4 which are connected to a rod I5 urgeddownwardlyby an adjustable Speeder spring I6 and actuating a valve thatregulates the flow of pressure fluid to and from the servo I2. Thusmanner to vary the propeller pitch and maintain the speed of the engineat a constant value determined by the adjustment of the speeder springI6. Such adjustment may be effected by turning a pinion l'l meshing with'a rack on a movable abutment IIl engaging the spring.

To enable the speed setting of each slave enl gine to`be adjusted from aremote point of control, the pinion Il is adapted to be turned by anelectric motor I8 mounted on the governor casing and acting throughspeed reduction gearing 20. This motor is the receiver of aself-synchronous electrical system controllable from a transmitter 2|located at a remote point of control, the pilots cabin in the case of anairplane. Herein, the electrical receiver I8 is of the step motor typehaving a permanently magnetize-d rotor 22 adapted to occupy any one oftwelve well defined angular positions according to the combination of 0direct current potentials applied to three sets Aof distributed windings23 on the motor stator 2l. When these windings are deenergized, therotor will come to an abrupt stop and be held magnetically.

Operation of the step motor in one direction or the other is effected byturning the shaft of the transmitter 2I which is a commutator switchherein shown as comprising angularly spaced segments 26 engaged bycontacts 2l which are arranged in pairs respectively connected to thedifferent polar terminals of a battery 28 through conductors 29. Thesegments 2B are connected directly to the windings of the step motor I8through a ground and conductors 30. The construction of the step motoris such that as the switch shaft 25 turns in one direction, the windingsof the step motor will be energized in successive combinations causingthe rotor 22 to follow the movements of the switch shaft. Reverseoperation of the motor takes place when the rotor of the commutatorswitch 2| is turned in the opposite direction.

The speed of each slave engine S is compared with that of the masterengine M, and any difference is utilized to turn the correspondingcommutator switch 2l in a corresponding direction and by an amount suchas to correct for the speed deviation. Such speed matching is eiected bya diiferential motor or so-called differential Selsyn 3l comprising athree phase two pole stator and a three phase two pole rotor havingwindings 32 and 33, the rotor being fast on the shaft 25. The windings32 and 33 are energized by small permanent magnet generators representeddiathe governor operates automatically in a known srammatically at 35and respectively mounted on the engines M and S and driven thereby. Theconnections from the generator 85 of the master engine include switches36.

With both' windings of the differential motor energized and with theengines M and S running at the same speed. the frequencies of the twocurrent sources will be identical so that the shaft of the diil'erentialmotor will not turn, and, therefore, the commutator switch 2| will beidle. When the speeds of the master and slave engines are different, thefrequencies of the current supplied by the respective generators willdiffer proportionately, and the rotor oi' the ditlerential motor willturn in a direction determined by which frequency is higher.- Suchloperation of the motor and the commutator switch driven thereby willcontinue until the slave engine has, by operation oi.' the step motor I8and the speed correcting means associated therewith, been brought intosynchronism with the speed oi' the master engine M.

To enable the differential motor 3| to be disabled at certain times, asduring the adjustment of the engine speeds under manual control, theswitches 36 are connected to the armature of a magnetic relay 31. Whenthe latter is energized. the switches 36 will be opened, and suchenergization also results in opening of switches 38 therebydisconnecting the transmitter 2| from the receiving motor I8 of theslave engine S. At the same time, switches 38 are closed to complete anelectrical connection between the motor I8 and conductors 40 leadingfrom an auxiliary commutator switch 4| to the step motor of the governoron the master engine M.

For the purpose of adjustingr the speed settings of all of the governersI under manual control from the remote point, the shaft 42 oi thetransmitter or commutator switch 4| is connected through speed reductiongearing tothe shaft of a reversible motor 43 which runs in one directionor the other according to which of its windings 44 or 45 is energizedfrom the battery 28. The circuit for the winding 44 ls closed by aswitch 46 when a relay 41 is energized, while the winding 45 isenergized by closure of a switch 48 when a relay 49 is energized. Wheneither one of two switches 50 is closed, a circuit is completed forenergizing the relay 31, thereby disconnecting the commutator switch 2|from the step motor I8 and connecting the step motor of all of the powerunits to the commutator switch 4|. The speed adjusting motor 43 isstarted in one direction or the other by movement of a manually operablelever to a position corresponding to a newly selected speed settingwhere the lever is retained as by friction. Such movement turns acontact arm 54 to close a corresponding one of two switches 52, 53 andcorrespondingly turn an arm 55 carrying the insulated contacts of theseswitches. The corresponding one of the relays 41, 49 is thus energized,and the motor 43 is started and continues to run in the proper directionuntil a follow-up mechanism including speed reduction gearing 56 and aheart-shaped cam 58 allows the arm 55 to move and open the then closedcontrol switch, whereupon the motor 43 will be stopped automatically. Bycorrelating the gear train 20 and the gear train 56 between the motor 43and the cam 58, the range of motion of the hand lever 5| will correspondto the range of speed adjustment of the governors I0 so that the latterwill, after each change in the setting of the lever 5|, be adjusted byits motor actuator for the maintenance of a corresponding engine speed.

In response to deenergization of both of the relays 41 and 48 as thegovernors become adjusted to the new speed, the switches 5l will againbe opened. This results in deenergization oi the relay 31 therebydisconnecting the step motors from the adjusting commutator switch 4|and placing only the slave motors I8 under the control oi thesynchronizing commutator switch 2|. Manual control is thus withdrawn andthe synchronizing control is restored automatically.

It will be observed from the foregoing that except for the generators 34all of the parts oi' the automatic synchronizing control and themanually controllable speed adiusters up to and including thetransmitters 2| and 4| may be located at a point of control, such as thepilot station in an airplane, which is remote Airom the engines M- and Sor any additional slave engines which may also be controlled. All oithese parts are housed in a casing 68 (Fig. 2) along with' the parts,that is the differential motor 2i, the commutator switch 2 I, and therelay 81, which would be duplicated for each additional slave engine Sto be synchronized with the master. The step motors I8 for suchadditional engines would be adapted for energization from the commonswitch 4| dur ing manual adjustment of the speed settings or by theirown commutator switch 2| during automatic synchronizing.

In accordance with the present invention, means is located at the remotecontrol point which operates to limit to a relatively small part of thespeed range the extent to which the speed of the slave engine or enginesmay be decreased while under the automatic synchronizing control. Thus,if the master engine should slow down or fail, the possibility of theautomatic synchronizing control reducing the speeds of the slave enginesto an objectionable degree is avoided and optimum safety in theoperation of an airplane is thereby assured.

The limiting means above referred to is a range to act positively on thedriving connection between each differential motor 3| and the commutatorswitch 2| driven thereby. It includes relatively rotatable members 6|and 62 having a limited lost motion connection between theml The member6I is a gear journaled on a shaft 63 in the casing 60 and driven fromthe differential motor 3| through speed reduction gearing 64. The

gear thus turns back and forth at a reduced speed during normaloperation of the differential mo-v tor to eiect speed adjustments of theslave engine S and match its speed against that of the master engine M.

To avoid damage to the differential motor or the associated parts, aslip clutch 65, preferably of the friction type, is interposed betweenthe motor shaft 66 and the drive pinion 61 oi the gearing, When thepinion is held against turning. the clutch will slip permittingoperation oi the differential motor.

The other member 62 of the movement limiting means is a disk journaledon the hub of the gear 6| and releasably held against rotation. This isaccomplished by a brake in the form of a pawl 68 pivoted on the casing6|) and constantly urged by a spring 69 against the toothed periphery 14of the disk, thereby locking the latter positively against turning. Thepawl constitutes the armature of an electromagnet 1I which, whenerergized, withdraws the pawl so as to release the disk 62. For apurpose to appear later. the coil of the magnet is connected in parallelwith the relay 31 previously described so as to be energizedautomatically in response Vto disabling of the automatic synchronizingcontrol preparatory to readjustment o! the engine speeds under thecontrol oi.' the hand lever ll. Conversely, when the manual control iswithdrawn and automatic synchronizing restored. the magnet isdeenergized and the brake reapplied,

The lost motion connection between thegear Il and the disk 02 is formedin the present instance by an arcuate slot 12 in the gear and a pin 12received in the slot and projecting from the disk l2. The disk and gearare thus adapted to turn relative to each other through a hal!revolution which, by proper selection of the gearing, corresponds toonly a small fraction of the total speed range through which the enginesmay be adjusted. For example, the lost motion may correspond to 150 R.P. M. so that when the pin 13 is centered in the lost motion slot 12 asshown in Fig. 4, the slave engine speed may be either increased ordecreased 75 revolutions before the slack in the lost motion is taken upand further speedadjustment of the slave engine prevented by thepositive action or the then locked disk 82.

To equalize the permissible speed adjustment of each slave engine inboth directions following each manual readjustment oi' the engine speed.means isv provided for centering the disk l2 relative to the slack inthe lost motion connection whenever the disk is released preparatory tomaking a manual readjustment of the engine I speed. This means comprisesa torsion spring 14 coiled around and fastened at one end to the hub ofthe gear 6I, the other end being secured to the pin 1l. When the pin iscentered in the slot 12. the spring will not be stressed. Turning of thegear 6| in either direction away from this centered position stressesthe spring so that whenever the magnetic brake is released, the disk 62will be turned by the spring andcentered relative to the gear as shownin Fig. 4.

It will be apparent that the permissible rotation of the commutatorswitch 2| by the differential motor Il is limited positively accordingto the length of the lost motion connection described above. Thus,during operationof the automatic synchronizing control, the slave enginemay follow the master only through a comparatively small number oi'revolutions, for example 75, before the transmitter 2| is disabledv bybeing blocked against further turning. Accordingly, ii the master engineM should failand thereby slow down. the speed of the slave engineslwould not be reduced to an objectionable degree. Optimum safety is thusachieved in the use of the automatic synchronizing control onmultiengine aircraft.

Provision is made for recentering the parts of the range limiting meansabove described as an incident to each manual speed adjustment so thatthe limiting means will be conditioned to allow equal speed adjustmentoi' the slave engine in either direction under the ensuing automaticsynchronizing control. That is to say, the speed of the slave engine maybe increased or decreased by 75 revolutions. In this way, thepossibility oi the range limiting means interfering with normaloperation of the automatic control is minimized. and at the same time.the possibility oi' the automatic control disabling a slave engine iseliminated.

Such recentering is accomplished by energizing the brake magnets 1|automatically whenever the manually controlled adjusting motor 4l isrunning, thereby releasing the member, that is the disk I2, whichnormally limits the range of the synchronized adjustment. ual control iswithdrawn and automatic synchronizing restored. the magnets are againdeenergized and the brake pawls el reengaged with teeth on the disk 82so as to render the range limiting means again operative.

I claim as my invention:

l. For synchronizing two rotary power units, the combination ofspeed-correcting means adapted to be associated with one of said units,means by which said speed-correcting means may be actuated automaticallyin accordance with speed deviations between said units including arotary differential motor, two members one driven by said motor andhaving a limited lost motion connection with the second member,yieldable means tending to center said second member in the range oi thelost .motion, braking means for holding said second member releasablyagainst movement, an auxiliary means operable under manual control foreffecting separate selective adjustment of said speed-correcting means.and means controlled by said auxiliary means and operable automaticallyto maintain said brake applied during operation oi' saidspeed-correcting means by said automatic means and to hold the brakereleased during operation of the speedcorrecting means under the controlo! said auxiliary means.

2. For synchronizing two rotary power units, the combination ofspeed-correcting 'means adapted to be associated with one .of saidunits, means by which said speed-correcting means may be actuatedautomatically in accordance with speed deviations between said unitsincluding a rotary diilerential motor, two members one driven by saidmotor and having a limited lost motion connection with the secondmember, yieldable means tending to center said second member in therange ot the lost motion, braking means for holding said second memberreleasably against movement, an auxiliary means operable under manualcontrol for effecting separate selective adjustment of saidspeed-correcting means, and means operable automatically as an incidentto operation of said auxiliary means to release said braking means andpermit automatic centering oi said second member by said yieldablemeans.

3. For synchronizing two rotary power units, the combination ofspeed-correcting means adapted to be associated with one oi said units,means by which said speed-correcting means may be actuated automaticallyin accordance with speed deviations between said units two relativelyrotatable members one moved in accordance with the automatic adjustmentsoi said speed-correcting means and having a limited lost motionconnection with the second member, yieldable means tending to centersaid second member within the range of the lost motion. electromagneticbraking means for holding said second member releasably againstmovement. an auxiliary means operable under manual control for eiectingseparate selective adjustment oi said speed-correcting means, and meansby which the energization and deenergization of said electromagneticbraking means may be controlled to maintain said brake applied duringoperation of said speed-correcting means by said automatic means and tohold the brake released during operation oi.' the speedcorrecting meansunder the control of said auxiliary means.

4. In -a system for synchronizing two rotary power units, thecombination o! means for com- When the manparing the rotational speedsof said units including a rotary dinerential motor, speed-correctingmeans for one of said units having a rotary driven connection with saidmotor, two rotary members one rotated in unison with said driveconnection, an electromagnetic brake operatively associated with thesecond rotary member and energizable and deenergizable selectively tohold the latter member or to release the member, means providing a lostmotion connection between said members permitting oi' limited relativeturning therebetween, and spring means yieldably resisting turning ofsaid second member relative to the rst member in either direction awayfrom a position centered within the range o! lost motion between saidmembers.

5. In a system for synchronizing two rotary power units, the combinationof means for comparing the rotational speeds of said units, including arotary differential motor, speed-correcting means for one of said unitscontrolled by said comparing means, two rotary members one rotated inunison with said correcting means, a brake operatively associated withthe second rotary member and adapted when applied and released torespectively hold the latter member or to release the member, meansproviding a lost motion connection between said members permitting oflimited relative turning therebetween, and means yieldably resistingturning of said second member relative to the iirst member in eitherdirection away from a position centered within the range of lost motionbetween said members.

6. In a system for synchronizing two rotary power units, the combinationoi means for comparing the rotational speeds of -said elements includinga rotary differential motor, speed-correcting means having a rotarydrive connection with said motor, means associated with said connectionand positively operable to limit the range of operation of thespeed-correcting means thereby in opposite directions relative to apredetermined centered relation, means by which said limiting means maybe released, and means operable automatically as an incident to suchrelease to center said limiting means and thereby equalize thepermissible extent of operation of said motor in either direction.

7. In a system for synchronizing two rotary power units, the combinationof means for comparing the rotational speeds of said units including arotary diiIerential motor, an electrical transmitter. a rotary drivingconnection between said motor and said transmitter speed-correctingmeans for one of said units including selfsynchronous electricalreceiver selectively ener- 8 sized by said transmitter. two rotarymembers one rotated in unison with said drive connection,

means operatively associated with the second rotary member for holdingthe member against rotation or releasing the member and means providinga lost motion connection between said members permitting of limitedrelative turnin therebetween.

8. In a system for synchronizing two rotin' power units, the combinationof means for comparing the4 rotational speeds oi said umts including arotary diiferential motor, an electrical transmitter, a rotary drivingconnection between said motor and said transmitter, speed-correctingmeans for one o! said units including a seli-synchronous electricalreceiver selectively energized by said transmitter. and means associatedwith said driving connection and operable to limit the extent ofrotation thereof by said diiierential motor.

9. In a system for synchronizing two rotary elements, a speed adjusterfor one oi' said elements, a reversible motor actuator therefor, a mainrotary electrical transmitter for energizing said motor, a differentialelectric motor for driving said transmitter, releasable means iorlimiting the range of rotation of said transmitter in oppositedirections by said differential motor, and means operable upon releaseof said last mentioned means to establish a centered relation betweensaid motor and said transmitter whereby to permit of equal rotation orthe transmitter in either direction.

10. In an automatic synchronizing control, the combination of, speedcomparing means including a rotary differential motor, speed-correctingmeans, driven by said motor, two members one driven by said motor andhaving a limited lost motion connection with the second member.yieldable means tending to turn said second member relative to the rstmember and establish a predetermined positional relation therebetween,means for holding said second member releasably against movement, andmeans controlling the release of said last mentioned means.

l1. In an automatic synchronizing control, the combination of, speedcomparing means, speedcorrecting means, having a driving connectiontherewith so as to be actuated thereby, means associated with saidconnection for positively limiting the extent of operation of thespeed-correcting means, andA means by which said limiting means may berendered operative and inoperative.

JAMES W. BRAKE.

